Alternate Names: Pregnancy sonogram; Obstetric ultrasonography; Obstetric sonogram; Ultrasound - pregnancy

How Performed: You will be lying down for the procedure. A clear, water-based conducting gel is applied to the skin over the area being examined to help with the transmission of the sound waves. The ultrasound transducer (a hand-held probe) is then moved over the abdomen and pelvis. This is the conventional transabdominal technique.

How To Prepare: You will need to drink 2 to 3 glasses of liquid 1 hour before the test. You may not urinate before the examination.

How It Feels: There may be some discomfort from the full bladder. The conducting gel may feel slightly cold and wet.

Risks: There is no documented biologic effect on patients and their fetuses with the use of current ultrasound techniques. No ionizing radiation is involved.

Why Performed:

There is no definitive rule as to the number of scans a woman should have during her pregnancy. Some physicians will order an ultrasound when an abnormality is suspected on clinical grounds, while others advocate screening ultrasounds. You should consult your health care provider to determine the most appropriate scanning schedule for you.

Scans may be performed in the first trimester to:

• Confirm a normal intra-uterine pregnancy
• Assess fetal age
• Exclude abnormalities such as ectopic pregnancies or threatened abortion
• Assess fetal heart activity
• Determine the presence of multiple pregnancies
• Identify abnormalities of the placenta, uterus, and other pelvic structures

Scans may also be obtained in the second and third trimesters to:

• Assess fetal age, growth and position
• Identify congenital malformations
• Exclude multiple pregnancies
• Evaluate the placenta, amniotic fluid, and remaining structures of the pelvis

Some centers are now performing a scan at around 13-14 weeks of pregnancy to measure the thickness of the "nuchal fold" (skin on the back of the fetal neck), also known as nuchal translucency, for the purpose of evaluating the risk for Down Syndrome.

The total number of scans will vary depending on whether a previous scan has detected abnormalities that require follow-up assessment.

Normal Values: The fetus and associated pelvic structures are normal in appearance.

Abnormal Results:

Abnormal ultrasound results may be due to some of the following conditions:

• Ectopic pregnancy
• Multiple pregnancies
• Fetal death
• Abnormalities of fetal position
• Congenital malformations
• Amniotic fluid problems, including oligohydramnios and polyhydramnios
• Placental abnormalities, including placenta previa and placental abruption
• Intrauterine growth retardation
• Tumors of pregnancy, including gestational trophoblastic disease
• Additional abnormalities of the ovaries, uterus, and remaining pelvic structures

Cost:

Special Considerations: Transvaginal ultrasound scanning may be performed with the probe placed in the vagina of the patient. This technique often complements conventional ultrasound techniques by providing better anatomic detail. Consult your health care provider to determine which technique is most appropriate for you.